The present invention relates to an inductive coupler which is operable by electromagnetic induction to transfer electrical power for charging a propulsion battery of an electrically powered vehicle. More specifically, it relates to a battery charging apparatus which can compensate for slight positioning error of the vehicle with respect to primary charging equipment at a ground charging station.
A battery charging system is known in the art which includes an inductive coupler configured in the form of a transformer mechanism and operable to transfer electrical energy for charging a battery of an electric vehicle from a primary charging equipment disposed within or on the floor of a ground battery charging station.
For example, Publication of Unexamined Japanese Patent Application No. 63-87136 (1988) discloses an apparatus comprising a secondary core and coil assembly disposed on the bottom of an electrical vehicle and a primary core and coil assembly located on the floor of a battery charging station, wherein the vehicle is driven carefully to locate the primary assembly correctly with respect to the primary assembly on the floor so that the primary and secondary assemblies are engaged appropriately or inductively coupled.
With the above apparatus, however, it has been found difficult to position the secondary assembly as desired relative to the stationary primary assembly, with the primary and secondary cores engaged or mated with only a small gap formed therebetween. It is known in the art that the presence of a core-to-core gap causes inductance leakage affecting-the electromagnetic induction efficiency and hence efficient battery charging operation. With the above apparatus, therefore, poor efficiency in battery charging was inevitable.